CVE-2022-49124 (GCVE-0-2022-49124)

Vulnerability from cvelistv5 – Published: 2025-02-26 01:55 – Updated: 2025-12-23 13:22
VLAI?
Title
x86/mce: Work around an erratum on fast string copy instructions
Summary
In the Linux kernel, the following vulnerability has been resolved: x86/mce: Work around an erratum on fast string copy instructions A rare kernel panic scenario can happen when the following conditions are met due to an erratum on fast string copy instructions: 1) An uncorrected error. 2) That error must be in first cache line of a page. 3) Kernel must execute page_copy from the page immediately before that page. The fast string copy instructions ("REP; MOVS*") could consume an uncorrectable memory error in the cache line _right after_ the desired region to copy and raise an MCE. Bit 0 of MSR_IA32_MISC_ENABLE can be cleared to disable fast string copy and will avoid such spurious machine checks. However, that is less preferable due to the permanent performance impact. Considering memory poison is rare, it's desirable to keep fast string copy enabled until an MCE is seen. Intel has confirmed the following: 1. The CPU erratum of fast string copy only applies to Skylake, Cascade Lake and Cooper Lake generations. Directly return from the MCE handler: 2. Will result in complete execution of the "REP; MOVS*" with no data loss or corruption. 3. Will not result in another MCE firing on the next poisoned cache line due to "REP; MOVS*". 4. Will resume execution from a correct point in code. 5. Will result in the same instruction that triggered the MCE firing a second MCE immediately for any other software recoverable data fetch errors. 6. Is not safe without disabling the fast string copy, as the next fast string copy of the same buffer on the same CPU would result in a PANIC MCE. This should mitigate the erratum completely with the only caveat that the fast string copy is disabled on the affected hyper thread thus performance degradation. This is still better than the OS crashing on MCEs raised on an irrelevant process due to "REP; MOVS*' accesses in a kernel context, e.g., copy_page. Injected errors on 1st cache line of 8 anonymous pages of process 'proc1' and observed MCE consumption from 'proc2' with no panic (directly returned). Without the fix, the host panicked within a few minutes on a random 'proc2' process due to kernel access from copy_page. [ bp: Fix comment style + touch ups, zap an unlikely(), improve the quirk function's readability. ]
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 27fbe5b28a2ffef171c6005f304ea4f80fcdcc01 , < ba37c73be3d5632f6fb9fa20b250ce45560ca85d (git)
Affected: 27fbe5b28a2ffef171c6005f304ea4f80fcdcc01 , < 8ca97812c3c830573f965a07bbd84223e8c5f5bd (git)
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    Linux Linux Affected: 2.6.19
Unaffected: 0 , < 2.6.19 (semver)
Unaffected: 5.17.3 , ≤ 5.17.* (semver)
Unaffected: 5.18 , ≤ * (original_commit_for_fix)
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{
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kernel/cpu/mce/core.c",
            "arch/x86/kernel/cpu/mce/internal.h"
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      ],
      "cpeApplicability": [
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          "nodes": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mce: Work around an erratum on fast string copy instructions\n\nA rare kernel panic scenario can happen when the following conditions\nare met due to an erratum on fast string copy instructions:\n\n1) An uncorrected error.\n2) That error must be in first cache line of a page.\n3) Kernel must execute page_copy from the page immediately before that\npage.\n\nThe fast string copy instructions (\"REP; MOVS*\") could consume an\nuncorrectable memory error in the cache line _right after_ the desired\nregion to copy and raise an MCE.\n\nBit 0 of MSR_IA32_MISC_ENABLE can be cleared to disable fast string\ncopy and will avoid such spurious machine checks. However, that is less\npreferable due to the permanent performance impact. Considering memory\npoison is rare, it\u0027s desirable to keep fast string copy enabled until an\nMCE is seen.\n\nIntel has confirmed the following:\n1. The CPU erratum of fast string copy only applies to Skylake,\nCascade Lake and Cooper Lake generations.\n\nDirectly return from the MCE handler:\n2. Will result in complete execution of the \"REP; MOVS*\" with no data\nloss or corruption.\n3. Will not result in another MCE firing on the next poisoned cache line\ndue to \"REP; MOVS*\".\n4. Will resume execution from a correct point in code.\n5. Will result in the same instruction that triggered the MCE firing a\nsecond MCE immediately for any other software recoverable data fetch\nerrors.\n6. Is not safe without disabling the fast string copy, as the next fast\nstring copy of the same buffer on the same CPU would result in a PANIC\nMCE.\n\nThis should mitigate the erratum completely with the only caveat that\nthe fast string copy is disabled on the affected hyper thread thus\nperformance degradation.\n\nThis is still better than the OS crashing on MCEs raised on an\nirrelevant process due to \"REP; MOVS*\u0027 accesses in a kernel context,\ne.g., copy_page.\n\n\nInjected errors on 1st cache line of 8 anonymous pages of process\n\u0027proc1\u0027 and observed MCE consumption from \u0027proc2\u0027 with no panic\n(directly returned).\n\nWithout the fix, the host panicked within a few minutes on a\nrandom \u0027proc2\u0027 process due to kernel access from copy_page.\n\n  [ bp: Fix comment style + touch ups, zap an unlikely(), improve the\n    quirk function\u0027s readability. ]"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-12-23T13:22:08.276Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/ba37c73be3d5632f6fb9fa20b250ce45560ca85d"
        },
        {
          "url": "https://git.kernel.org/stable/c/8ca97812c3c830573f965a07bbd84223e8c5f5bd"
        }
      ],
      "title": "x86/mce: Work around an erratum on fast string copy instructions",
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      }
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2022-49124",
    "datePublished": "2025-02-26T01:55:03.188Z",
    "dateReserved": "2025-02-26T01:49:39.265Z",
    "dateUpdated": "2025-12-23T13:22:08.276Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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